1. Field of the Invention
The invention is a rear suspension design which can be incorporated into light weight racing frames such as are used by professional racing teams.
2. Summary of the Invention
Professional racing teams race some extremely rough courses including many sections paved with cobblestones. These can be extremely fatiguing and dangerous to the riders, causing many instances of loss of control of the bike and resultant crashes. For example, one race that is famous for the amount of rough surface conditions is the Paris-Roubaix.
These races can be very damaging to the riders and their equipment. They will sometimes use larger diameter tires than on normal courses in order to provide a little more cushion and more resistance to flatting on the harsh bumps. The drawback is that additional mass on the bike degrades its performance in several ways and the larger tires typically add additional weight to the bike. In addition, the road racing bike frames are typically made so as to be very close to the narrow racing tires. So it is usually possible to only put a slightly larger tire on. There usually is not clearance for a substantially larger tire. The side pull type brakes that road racing bikes use also preclude a much larger tire. They do not have adequate reach adjustment or tire clearance to fit larger road tires. So even if you designed more tire clearance into a frame, it would not be able to use this type of brake.
It is possible to use a different type of bike called a cyclo-cross type which does allow the use of significantly larger tires. These bikes are intended for off road use and utilize a different type of braking system called cantilevers which allow for a larger tire. So on these bikes the frame and the brakes have more clearance for larger tires.
But most of the road racing teams like to stay on their road racing bikes, even for the rougher road conditions. They are used to the fit and handling of their personal bike and don't like to change the type of bike.
In addition to the fatigue, the rough courses cause substantial loss of energy to the bumps and result in significantly lower bike speeds than the similar amount of effort on a smooth course would achieve. The vertical up and down motion which is beating up the rider and causing loss of wheel traction comes out of the pedaling energy supplied by the rider.
Some road racing teams have used front suspension forks on these rougher courses. These forks are typically add at least 1 kilogram of mass to the bike. This is a large amount of weight to add and a considerable detriment to the bikes performance on a moderate to smooth road. As they have a significant amount of stiction, the static friction resulting from the sliding seals and bearings which must be overcome before the suspension can begin to move, they are only partially effective at attenuating the front wheel shocks. They provide noticeable cushioning of the hands of the rider, but not much for the saddle or feet, where most of the riders weight is. Most of the weight of the cyclist, and the all of the cyclists forward driving force is located at the rear wheel. So suspension and better traction is likely to be at least, if not more useful on the rear than on the front wheel. In addition, the sliding type front forks have a tendency to move up and down with each pedal stroke, unless the stiction is high enough to prevent it. This motion wastes the rider's energy. But higher stiction reduces the amount of road shock that the front fork attenuates.
This is especially evident in a sprint, when the pedaling forces are larger, so the weight shift from front wheel to rear wheel with each pedal stroke is greater, and more of the riders weight is moved forward to the front wheel as he leans forward or stands up. As a result, the use of front suspension forks in these types of events has had very limited success.
The invention is intended to attenuate the amplitude of deflections that the rider feels, both in the feet and seat. This will reduce fatigue in the rider, especially over a longer course. The invention is further intended to improve the adhesion of the tires to the pavement, by reducing the amount of time they are not in contact with the road surface and reducing the variation or amplitude of forces between the tire and the ground.
The invention provides a limited amount of very supple rear wheel suspension travel, about 1 to 1.8 cm in the preferred configuration, while retaining the light weight of the some of the lightest professional level bicycle racing frames, and retaining sufficient structural rigidity to control the out-of-plane deflection of the overall frame and the rear wheel of the bike which lead to loss of efficiency and control of the bike.
The invention is adaptable to be used in a variety of bicycle frames including molded fiber reinforced plastic frame such as FIG. 1-3, or a metal frame, such as the welded and heat treated aluminum type of frame as shown in FIG. 7-10. One of ordinary skill in the art will understand that the invention can be adapted regardless of the particular frame material, whether fiber reinforced plastic, metal such as steel, aluminum or Titanium, or a combination of materials. Similarly, one of ordinary skill will be able to adapt component mounting such as the brake fixing nut which also retains the shock.
3. Description of Related Art
Some of the prior art suspension designs used curved seatstays. The bend(s) destabilize the seat stay tubes, and cause it to flex more when an axial load is applied, either by the riders weight or by a momentary bump impact. Unfortunately, the bends also greatly reduce the capability of a given tube to support an axial load. Thus, the bent seat stays must be made heavier than normal to provide adequate frame structure. One design uses a single large radius bend in the seatstays, but the amount of flex under compression is limited by a layer of polymer and a stainless steel strap under tension. This of course adds considerable weight to the overall structure, while providing less benefit than the current invention.
Prior art devices either used mechanical pivots to allow the rear wheel to move vertically with respect to the rest of the frame and the rider, or they utilized very vertically flexible members for the chainstays, for example, in order to allow a large amount of deflection from their resting position. Some of these have metal chainstays but which have been reinforced and flattened horizontally so they are not stiff in the vertical direction, but still torsionally and laterally rigid. Or they have had sections of the chainstay where the metal is replaced by a flat fiberglass spring, for example.
U.S. Pat. No. 6,406,048 issued to Castellano on Jun. 18, 2002. This patent is entitled “Pivotless Rear Suspension System For Bicycles”. According to Castellano, utilization of tubular type chainstays precludes a useful amount of suspension travel. Castellano further states that the alignment between the upper and lower portions of the wishbone must be free to move angularly in order to allow operation of the particular shock arrangement of the '048 patent. This patent is incorporated by reference.
Adding pivots or reinforcing and substantially reshaping the chainstays, or adding flat springs to the chainstays all typically add weight to the bike. And since the resultant structure is not very rigid vertically, in order to take a large deflection in one direction for many cycles without fatigue, the compressive spring must be designed to take most of the compressive loads, making it heavier. There also needs to be a negative spring and mechanism for activating it included in these designs, which again adds weight and complexity.